Hydroformylation Process for Pharmaceutical Intermediate

ABSTRACT

The invention relates to an improved process for the preparation of an advanced synthetic intermediate of ACE inhibitors. In one aspect, the present invention is based on a novel process for the preparation of an aldehyde of formula (I), wherein (N) PrG  is a protected amino group, R is an alkyl or aralkyl group and X 1-4  are each independently H or a non-reacting substituent, which comprises hydroformylation of an α-olefin of formula (II), by reaction with syngas (CO/H 2 ) in the presence of, as catalyst, a group VIII transition metal complex of a phosphorus-containing ligand. Aldehyde (I), the product of linear hydroformylation, is formed in preference to aldehyde (III). In another aspect of the invention, α-olefin (II) is a novel composition. The process to convert (II) to (I) enables an efficient manufacturing route to MDL 28,726 and analogues.

FIELD OF THE INVENTION

The invention relates to an improved process for the preparation of anadvanced synthetic intermediate of ACE inhibitors.

BACKGROUND TO THE INVENTION

The tricyclic acid MDL 28,726 (1) is a key intermediate in the synthesisof ACE inhibitors MDL 27,210, MDL 100,240 and related analogues, whichalso possess inhibition activity against neutral endopeptidase (NEP).There is a requirement for an improved synthetic route to MDL 28,726that provides favourable process economics for large scale commercialoperation; this problem is addressed by the present invention.

The original synthetic route to (1), reported by Flynn et al. (J. Am.Chem. Soc., 1987, 109, 7914) culminates in a stereoselectiveacyl-iminium ion induced cyclization to form the tricyclic ring systemof (1). This reaction also forms the basis of an improved route reportedby Horgan et al. (Org. Proc. Res. Dev., 1999, 3, 241), in which thedesired stereoisomer of the cyclization substrate (2) is prepared moreefficiently via an enzymatic resolution of a hydroxynorleucinederivative early in the synthesis. In contrast, the Flynn synthesisrequires preparative HPLC separation of a 1:1 mixture of (2) and itsopposite diastereoisomer and also requires a low temperature ozonolysisstep. Although demonstrated at on pilot plant scale, the Horgansynthesis has certain features which render it unsuitable for commercialoperation. In particular the route requires a low temperature Swernoxidation to produce (2) via the intermediate aldehyde (3), which is notideal for large scale preparations, as it typically involves cryogenicreaction conditions, control of dimethylsulfide by-product emissions,expensive reagents such as oxalyl chloride and variable yields.

Hydroformylation of monosubstituted olefins (4; also known asα-olefins), catalyzed by group VIII transition metal complexes ofphosphorus containing ligands, is a synthetically useful reaction,provided that high selectivity between the linear (5) and branched (6)aldehyde products can be achieved (Scheme 1). Typically, it ispreferable that the ratio of the desired product to its regioisomer isat least 80:20, more preferably at least 90:10. In an ideal case,complete regioselectivity is achieved in combination with efficientsubstrate conversion. For cases where the linear regioisomer (5) isdesired, a number of different catalysts have been designed for thispurpose (for a review, see Recent Advances on Chemo-, Regio- andStereoselective Hydroformylation, Breit and Seiche, Synthesis, 2001, 1,pp 1-36). Rhodium complexes of bisphosphite ligands provide one of thebest known classes of linear-selective hydroformylation catalysts (U.S.Pat. No. 4,668,651 and U.S. Pat. No. 4,769,498). Representative ligandsfrom this class include BIPHEPHOS (7) and the bisphosphite (8). A morerecent series of bis-chelating ligands designed for linear selectivehydroformylation is reported in WO2004035595; rhodium complexes of theseligands give particularly high linear:branched product ratios for simpleα-olefins such as 1-octene and high catalytic activity to enableefficient substrate conversion at low catalyst loading.

The methodology for hydroformylation of monosubstituted olefins wasoriginally designed for relatively simple, unfunctionalized olefins suchas 1-alkenes, e.g. 1-propene, 1-octene and styrene. Subsequently, anumber of applications to more complex α-olefins, leading to highervalue products, have been reported. As the structural complexity of anα-olefin increases, for example through the presence of functionalgroups (Cuny and Buchwald, J. Am. Chem. Soc., 1993, 115, 2066), subtlechanges in the substrate can have a profound effect on the selectivitythat is achievable with a given hydroformylation catalyst. Thus, theidentity of a suitable catalyst for a particular substrate becomes muchless predictable. For example, this is evident by comparing a processreported by Ojima et al (J. Org. Chem., 1995, 60, 7078) with anotherreported by Teoh et al (New. J. Chem., 2003, 27, 387). In the Ojimaexample [Reaction (a) in Scheme 2], a Rh-(BIPHENPHOS) catalyst provides100% regioselectivity for the allyl glycinate substrate (9). In thisprocess, the initially formed linear aldehyde, corresponding to (5) inScheme 1, undergoes spontaneous cyclization to form a heterocyclicproduct. In the Teoh example [Reaction (b) in Scheme 2] use of the samecatalyst on substrate (10), differing from (9) only in the nature ofester and N-acyl groups, a 2:1 mixture of regioisomers is produced.Because of the formation of a large amount of branched regioisomerrequiring separation from the desired linear regioisomer, Reaction (b)is not a synthetically useful process.

SUMMARY OF THE INVENTION

In one aspect, the present invention is based on a novel process for thepreparation of an aldehyde of formula (I), wherein (N)_(PrG) is aprotected amino group, R is an alkyl or aralkyl group and each of X¹⁻⁴is independently H or a non-reacting substituent, which compriseshydroformylation of an α-olefin of formula (II), by reaction with syngas(CO/H₂) in the presence of, as catalyst, a group VIII transition metalcomplex of a phosphorus-containing ligand. Aldehyde (I), the product oflinear hydroformylation, is formed in preference to aldehyde (III).Optional recovery and efficient recycle of the intact hydroformylationcatalyst and the ease of direct product isolation further characterizethe operation of this manufacturing process.

In another aspect of the present invention, the process to convert (II)to (I) further enables a novel and efficient manufacturing route to MDL28,726 and analogues, as key precursors to dual ACE-NEP inhibitors.Prior to this invention, the preferred methods of preparation for suchbioactive compounds would have used a protracted linear synthesis viaacetal-protected L-allysine (for representative references, see U.S.Pat. No. 6,174,707, U.S. Pat. No. 5,508,272 and U.S. Pat. No.6,166,227), or a hydroxynorleucine derivative with a subsequentoxidation to the aldehyde as described by Horgan et al. (Org. Proc. Res.Dev., 1999, 3, 241).

In yet another aspect of the present invention, the α-olefin (II) is anovel composition.

DESCRIPTION OF THE INVENTION

In the hydroformylation process of the invention, R in compounds (I) and(II) is selected preferably from the group consisting of methyl, ethyl,n-propyl, n-butyl, benzyl and benzhydryl. More preferably, R is methyl.Preferably, the protected amino group (N)_(PrG) is chosen to be stableto acid treatment. More preferable (N)_(PrG) is a cyclic imide and mostpreferably it is N-phthalimide. Commonly, each of X¹⁻⁴ is H although itwill be appreciated by those skilled in the art that the process of thepresent invention will be applicable in cases where any of X¹⁻⁴ is anon-reacting substituent, i.e. being stable under hydroformylationconditions, for example as taught by Cuny and Buchwald, J. Am. Chem.Soc., 1993, 115, 2066.

The catalyst for the process is selected such that the ratio of theproduct (a) to its branched regioisomer (III) is at least 80:20, morepreferably is at least 90:10 and ideally is at least 98:2, or higher.Suitable catalysts for this purpose comprise a group VIII transitionmetal complexed to a phosphorus-containing ligand. Preferably, thetransition metal is selected from the group consisting of rhodium (Rh),cobalt (Co), iridium (Ir), ruthenium (Ru), iron (Fe), nickel (Ni),palladium (Pd), platinum (Pt), and osmium (Os). More preferably thetransition metal is either Rh, Co, Ir, or Ru and most preferably it isRh. Preferably, the ligand is selected from the group comprisingtriorganophosphines, triorganophosphites, diorganophosphites, andbisphosphites. More preferably, the ligand is a bisphosphite, andtypically contains the partial formula (IV). Representative ligands ofthis type, having utility in the process of the invention, are selectedfrom the group including BIPHEPHOS (V), (VI) and the unsymmetricalbisphosphite (VII) in which R is H, CH₃, OCH₃, or OC₂H₅.

For operation of the process of the invention, a pre-formed,storage-stable complex of the transition metal and phosphorus-containingligand may be employed, although more commonly, the catalyst complex isprepared in solution prior to use, and said solution is combined in thereaction vessel with a solution of the α-olefin substrate (II) and thesyngas reagent. Preparation of the solution of catalyst complex entailsreaction of the ligand with a precursor complex containing thetransition metal, optionally using a molar excess of ligand such thatuncomplexed ligand is present once all of the precursor complex isconsumed. Additional ligand may also be added during the course of thehydroformylation reaction. Where the transition metal is Rh, theprecursor complex is preferably Rh(acac)(CO)₂. Preferably the molarratio of ligand:transition metal is in the range of about 1:1 to 100:1,and more preferably this ratio is in the range of about 1.3:1 to 3:1.

The reaction conditions for effecting hydroformylation of the α-olefinsubstrate (II) can be chosen from any of those conditions conventionallyused and known for such processes. Generally, the hydroformylationprocess temperature is greater than about 25° C., preferably greaterthan about 35° C., and more preferably greater then about 45° C.Generally, the hydroformylation process temperature is less than about110° C., preferably less than about 100° C. and more preferably lessthan about 90° C. The hydroformylation process may be conducted as abatch or continuous process. Preferably, the total pressure of hydrogenand carbon monoxide is less than about 2000 psia (13,790 kPa), and morepreferably less than about 1500 psia (10,342 kPa). More specifically,the carbon monoxide partial pressure of the hydroformylation process ofthis invention is typically greater than about 10 psia (69 kPa),preferably greater than about 20 psia (138 kPa). The carbon monoxidepartial pressure of the hydroformylation process of this invention istypically less than about 1000 psia (6,895 kPa), preferably less thanabout 750 psia (5171 kPa). The hydrogen partial pressure is typicallygreater than about 5 psia (35 kPa), preferably greater than about 10psia (69 kPa). The hydrogen partial pressure is typically less thanabout 1000 psia (6,895 kPa), preferably less than about 750 psia (5171kPa). In general, the H₂/CO molar ratio of gaseous hydrogen to carbonmonoxide may be greater than about 1/10, and preferably, equal to orgreater than about 1/1. The H₂/CO molar ratio may be less than about100/1, and preferably, equal to or less than about 10/1.

The hydroformylation process of this invention is also preferablyconducted in the presence of an organic solvent that solubilizes theGroup VIII transition metal complex catalyst. Any suitable solvent ormixture of solvents that does not interfere unduly with thehydroformylation and product-catalyst separation process can be used,including those types of solvents commonly used in prior arthydroformylation processes. Isolation of aldehyde (I) can beaccomplished by a non-aqueous phase separation procedure in whichaldehyde (I) is extracted into a polar organic solvent and residualmetal-containing complexes are extracted into a non-polar organicsolvent. This procedure is described more fully in U.S. Pat. No.5,952,530, the contents of which are incorporated herein by reference.Alternatively, the aldehyde (I) may by subjected to one or moredownstream chemical processes, without prior isolation from thehydroformylation reaction mixture.

Another aspect of the present invention provides a novel composition,α-olefin of formula (II), wherein (N)_(PrG) is a protected amino group,R is an alkyl or aralkyl group and each of X¹⁻⁴ is independently H or asubstituent that is unreactive under hydroformylation conditions.Preferably, R in compound (II) is selected from the group consisting ofmethyl, ethyl, n-propyl, n-butyl, benzyl and benzhydryl. Morepreferably, R is methyl. Preferably, the protected amino group (N)^(PrG)in compound (II) is chosen to be stable to acid treatment. Morepreferable (N)_(PrG) is a cyclic imide and most preferably it isN-phthalimide. Preferably, each of X¹⁻⁴ is H.

In a preferred embodiment, the process of the present invention enablesan efficient synthetic route to MDL 28,726 (Scheme 3). Once the aldehyde(Ia) has been made, this route comprises treatment with one or more acidreagents to effect sequentially (i) conversion of aldehyde (I) to5,6-didehydropipecolate (IXa) and (ii) cyclization of (IXa) to form MDL28,726 or its carboxylic ester precursor. Preparation of thehydroformylation substrate, α-olefin (IIa) wherein R is methyl, isachieved by coupling of reagents (X) and (XI), derived from(S)-phenylalanine and (S)-allylglycine respectively. In the context ofdisclosures in the prior art, notable features of the overall syntheticroute include the following:

-   -   (a) Swern oxidation is avoided.    -   (b) Complete control over all stereocentres is maintained        throughout the synthesis.    -   (c) Surprisingly for the substrate (IIa) containing a methyl        ester, a very high ratio linear:branched aldehyde products is        observed, when a Rh-BIPHENPHOS complex is used as the catalyst.        The presence of a t-butyl ester in the substrate is not        required. The resultant methyl ester-containing product (Ia) has        ideal solubility characteristics to enable clean separation from        catalyst residues according to the non-aqueous phase separation        procedure described above.

The invention is further illustrated by the following examples.

EXAMPLE 1 Preparation of N-phthaloyl (S)-phenylalanine acid chloride (X)

A 1-L round-bottom flask was charged with 50.19 g of (S)-phenylalanine,47.3 g of phthalic anhydride, 0.5 mL of triethylamine, and 500 mL oftoluene. The mixture was heated to reflux with stirring, and the waterremoved using a Dean Stark trap. After the water removal was complete,the mixture was cooled to ambient temperature, chilled in an ice bath,and the solid isolated by filtration to give a 103.4 g wet-cake of (IX)(80.3% solids, 83.0 g dry weight basis, 92.6% yield). A 60.47-g portionof the wet-cake was charged to a 1-L flask with 250 mL of toluene and 1mL of N,N-dimethylformamide. To the slurry was added dropwise 19 mL ofoxalyl chloride. After stirring overnight at ambient temperature, thesolvent was evaporated to give a 139.7 g residue. The residue wasdissolved in 200 g of ethyl acetate to give a 15 wt % solution of theacid chloride (X) in ethyl acetate.

EXAMPLE 2 Preparation of (S)-Allylglycine Methyl Ester Hydrochloride(XI)

A 250-mL round-bottom flask was charged 66.5 g of methanol, 4.45 g ofanhydrous hydrogen chloride, and 3.16 g of (S)-allylglycine. The mixturewas heated to reflux for one hour, then cooled for the addition of 10 mLof trimethylorthoformate. The solution was heated to reflux for sixhours, then cooled to ambient temperature and diluted with 50 mL oftoluene. The mixture was evaporated to a residue. An additional 50 mL oftoluene was added, and the solvent evaporated to a residue of 5.58 gcontaining (S)-allylglycine methyl ester hydrochloride (XI).

EXAMPLE 3 Preparation of(S)—N-[2-(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)-1-oxo-3-phenylpropyl)-allyl-(S)-glycineMethyl Ester (IIa)

To the 5.58-g residue of (S)-allylglycine methyl ester hydrochloride(XI) prepared above was added 19 g of ethyl acetate and 6 g ofacetonitrile. The mixture was chilled in an ice bath for the dropwiseaddition of 9.2 g of N-methylmorpholine. To the resulting mixture wasadded dropwise 63 g of the N-phthaloyl-(S)-phenylalanine acid chloride(X) in ethyl acetate solution prepared above. Following reactioncompletion, the mixture was diluted with 20 mL of water. The pH wasadjusted to 1 with 6.3 g of 37% hydrochloric acid, and the aqueous phasewas removed. Water (25 mL) was added, and the pH adjusted to 8.5 by theaddition of sodium bicarbonate. The aqueous phase was removed. Thesolvent was removed from the organic phase to give a 15.2 g residue. Theresidue was treated with 51 mL of 2-propanol, the mixture heated toreflux to give a solution, then cooled to give a slurry. The mixture waschilled in an ice bath and the solid collected by filtration, rinsedwith 5 mL of 2-propanol, and dried at 40° C. under vacuum to give 7.54 g(67% yield) of(S)—N-[2-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-1-oxo-3-phenylpropyl)-allyl-(S)-glycinemethyl ester (IIa). HPLC analysis indicated the purity was 99%.

EXAMPLE 4 Preparation of(S)-2-[(S)-2-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-1-oxo-3-phenylpropyl)-6-oxo-hexanoicacid methyl ester (Ia) Using a Rh-(VII) Complex as Catalyst

In a glove box, a THF (8.00 g) solution of Rh(acac)(CO)₂ (0.0188 g,0.0729 mmol) and N,N-diisopropylethylamine (0.252 g, 1.95 mmol)) wasprepared and added to the ligand (VII) wherein R is methoxy (0.100 g,0.0913 mmol; WO2004035595) in 7.00 g THF. Compound (IIa) (7.00 g, 17.2mmol) was dissolved in 15 g THF. The catalyst solution was charged intothe reactor and the compound (II) solution into a 35 mL substrate feedcylinder. The reactor and the cylinder were purged with 1:1 syn gas (90psi) three times. The reactor was then pressurized with 1:1 syn gas to40 psig and heated to 54° C. After stirring the catalyst solution at 54°C. for 15 minutes, the compound (II) solution was added into the reactorwith 90 psi 1:1 syn gas. The reactor was then fed with 1:1 syn gas froma 310 cc cylinder. Reaction time was recorded for every 6 psi gas uptakefrom the 310 cc syn gas cylinder. After 1 hour and 43 minutes, gasuptake stopped. The reaction solution was collected into a 250 mLSchlenk flask containing 10 mL of pentadecane under nitrogen. Afterevaporating the THF, acetonitrile (60 mL) and pentane (60 mL) wereadded. After stirring for 5 minutes, the acetonitrile phase wasseparated and extracted with pentane (3×20 mL). Acetonitrile wasevaporated to obtain 5.3 g (70%) off-white solid of (Ia). The productwas characterized by ¹H and ¹³C NMR, and HPLC analysis. The ratio oflinear to branched aldehyde was approximately 12:1.

EXAMPLE 5 Preparation of(S)-2-[(S)-2-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-1-oxo-3-phenylpropyl)-6-oxo-hexanoicacid methyl ester (Ia Using a Rh-(V) Complex as Catalyst

In a glove box, a THF (8.00 g) solution of Rh(acac)(CO)₂ (0.0149 g,0.0578 mmol) was prepared and added to the solution of BIPHENPHOS (V;0.0907 g, 0.1153 mmol) in 7.00 g THF. Compound (IIa) (7.00 g, 17.2 mmol)was dissolved in 15 g THF. The catalyst solution was charged into thereactor and the compound (II) solution into a 35 mL substrate feedcylinder. The reactor and the cylinder were purged with 1:1 syn gas (70psi) three times. The reactor was then pressurized with 1:1 syn gas to70 psi and heated to 65° C. After stirring the catalyst solution at 65°C. for 15 minutes, the pressure in the reactor was reduced to 65 psi andthe compound (II) solution was added into the reactor with 70 psig 1:1syn gas. The reactor was vented until all the feed solution was addedinto the reactor. The reactor was then fed with 1:1 syn gas from a 310cc cylinder. Reaction time was recorded for every 6 to 10 psi gas uptakefrom the 310 cc syn gas cylinder. After 2 hours, gas uptake stopped. Thereaction solution was collected into a 250 mL Schlenk flask containing10 mL of pentadecane under nitrogen. After evaporating about 90% of theTHF, acetonitrile (60 mL) and pentane (60 mL) were added. After stirringfor 5 minutes, the acetonitrile phase was separated and extracted withpentane (3×20 mL). Acetonitrile was evaporated to obtain 6.04 g (80%)white solid of (Ia). The product was characterized by ¹H and ¹³C NMR,analysis. The ratio of linear to branched aldehyde was approximately99:1.

EXAMPLE 6 Preparation of MDL 28,726

A 25-mL round-bottom flask was charged with 1.52 g of((S)-2-[(S)-2-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-1-oxo-3-phenylpropyl)-6-oxo-hexanoicacid methyl ester (Ia) and 2.7 g of ethyl acetate. One drop of methanesulfonic acid was added, and the mixture stirred at ambient temperature.After about one hour, a slurry had formed. The solid was isolated byfiltration and rinsed with 0.5 mL of ethyl acetate and dried at 40° C.under vacuum to give 0.74 g (51% yield) of(S)-1-[(S)-2-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-3-phenyl-propionyl)]1,2,3,4-tetrahydro-pyridine-2-carboxylicacid methyl ester (IXa). HPLC analysis indicated the material was 98%pure. Methyl ester (IXa) can be converted to MDL 28,726 by furthertreatment with acid, for example according to the procedure described byHorgan et al. in Org. Proc. Res. Dev., 1999, 3, 241.

1. A process for the preparation of an aldehyde of formula (I), wherein(N)_(PrG) is a protected amino group, R is an alkyl or aralkyl group andeach of X¹⁻⁴ is independently H or a non-reacting substituent, whichcomprises hydroformylation of an α-olefin of formula (II), by reactionwith syngas (CO/H₂) in the presence of, as catalyst, a group VIIItransition metal complex of a phosphorus-containing ligand.


2. A process according to claim 1, wherein each of X¹⁻⁴ is H.
 3. Aprocess according to claim 1, wherein R is selected from the groupconsisting of methyl, ethyl, n-propyl, n-butyl, benzyl and benzhydryl.4. A process according the claim 3, wherein R is methyl.
 5. A processaccording to claim 1, wherein (N)_(PrG) is stable to acid treatment. 6.A process according to claim 5, wherein (N)_(PrG) is a cyclic imide. 7.A process according to claim 6, wherein (N)_(PrG) is N-phthalimide.
 8. Aprocess according to claim 1, wherein the ratio of the product (I) toits branched regioisomer (III) is at least 80:20.


9. A process according to claim 8, wherein the ratio of the product (I)to its branched regioisomer (III) is at least 90:10.
 10. A processaccording to claim 9, wherein the ratio of the product (I) to itsbranched regioisomer (III) is at least 98:2.
 11. A process according toclaim 1, wherein the transition metal is selected from the groupconsisting of rhodium (Rh), cobalt (Co), iridium (Ir), ruthenium (Ru),iron (Fe), nickel (Ni), palladium (Pd), platinum (Pt), and osmium (Os).12. A process according to claim 11, wherein the transition metal isselected from the group consisting of rhodium (Rh), cobalt (Co), iridium(Ir), ruthenium (Ru).
 13. A process according to claim 12 wherein thetransition metal is Rh.
 14. A process according to claim 1, wherein theligand is selected from the group comprising triorganophosphines,triorganophosphites, diorganophosphites, and bisphosphites.
 15. Aprocess according to claim 14, wherein the ligand is a bisphosphite. 16.A process according to claim 15, wherein the bisphosphite contains thepartial formula (IV).


17. A process according to claim 16, wherein the bisphosphite isselected from the group consisting of compounds (V), (VI) and (VII)wherein R is H, CH₃, OCH₃, or OC₂H₅.


18. A process according to claim 17, wherein the bisphosphite iscompound (V).
 19. A process according to claim 1, wherein the catalystis generated in the reaction vessel by reaction of the ligand with aprecursor complex containing the transition metal, optionally using anmolar excess of ligand such that uncomplexed ligand is present once allof the precursor complex is consumed.
 20. A process according to claim1, wherein the transition metal is Rh and the precursor complex isRh(acac)(CO)₂.
 21. A process according to claim 20, wherein the molarratio of ligand:transition metal is in the range of about 1:1 to 100:1.22. A process according to claim 21, wherein the molar ratio ofligand:transition metal is in the range of about 1.3:1 to 3:1.
 23. Aprocess according to claim 1, wherein the reaction temperature is in therange of about 25° C. to 110° C.
 24. A process according to claim 23,wherein the reaction temperature is in the range of about 45° C. to 90°C.
 25. A process according to claim 1, which further comprisesconversion to a tricyclic acid of formula (VIII).


26. A process according to claim 25, wherein conversion to compound(VIII) comprises treatment with one or more acid reagents to effectsequentially (i) conversion of aldehyde (I) to 5,6-didehydropipecolate(IX) and (ii) cyclization of (IX) to form compound (VIII) or itscarboxylic ester precursor.


27. A process according to claim 26, wherein the aldehyde (I) isisolated from the hydroformylation reaction mixture prior to step (i).28. A process according to claim 27, wherein the process to isolatealdehyde (I) comprises a non-aqueous phase separation procedure in whichaldehyde (I) is extracted into a polar organic solvent and residualmetal-containing complexes are extracted into a non-polar organicsolvent.
 29. A process according to claim 26, wherein the aldehyde (I)is not isolated from the hydroformylation reaction mixture prior to step(i).
 30. A process according to claim 25, wherein the tricyclic acid isMDL 28,726


31. An α-olefin of according to formula (II) in claim
 1. 32. An α-olefinaccording to claim 31, wherein R is selected from the group consistingof methyl, ethyl, n-propyl, n-butyl, benzyl and benzhydryl.
 33. Anα-olefin according to claim 32, wherein R is methyl.
 34. An α-olefinaccording to claim 33, wherein (N)_(PrG) is stable to acid treatment.35. An α-olefin according to claim 34, wherein (N)_(PrG) is a cyclicimide.
 36. An α-olefin according to claim 35, wherein (N)_(PrG) is aN-phthalimide.